Protecting electronic circuits from unauthorized access is an important consideration when designing apparatus that may contain sensitive and/or confidential information, e.g., point of sale (POS) devices that collect confidential information about credit cards or bank account details when a purchase is being made.
Recently, security wraps have been used for the protection of such devices. The security wrap forms a part of the device's security system and detects an attempt to physically access the protected portion of the device. The security wrap physically covers the electronic components being protected, referred to as the parent device, which may be a portion of a PCB, the entire PCB or components like a smart card connector, a microprocessor and the like. The security wrap may be flexible so as to be able to be wrapped around the parent device, further reducing the opportunities to access the components.
The security wrap has one or more conductors connected between corresponding pairs of screen terminals, forming a security screen. The screen termninals are connected to terminals of an alarm circuit of the parent device. Severing a connector triggers an alarm condition. The function of the alarm circuit is not a part of the instant invention and depends on the security response of the device being protected which may range from a visual and/or audible indication, to shutting down of the device, disabling the device or in an extreme response to total destruction of the device or the components being protected.
Prior art security wraps are made with etched copper circuitry or flexible printed circuits (FPC). They can also be fabricated by additive method such as polymer thick film (PTF) technology using printed conductors. Typically the circuits consist of substrate, conductor layers, adhesive layer, and/or dielectric layers.
However, the use of x-ray detection methods can be used to reveal the conductor traces, the circuitry layout and the location of terminal contact points. With this information, hackers may use a drill or laser cutting to by-pass the security circuitry to access IC chips and other sensitive electronic components on the board.
Another problem with existing products is that a flexible security wrap is a relatively simple circuitry; a single layer conductor layout typically satisfies the design requirements. While in theory it is possible to use a thick metal plate to block x-ray detection, this method is not practical in point of sale (POS) devices due to weight, space and flexibility constraints. In order to improve the security coverage by conductors, one approach is to use double-layer or multi-layer circuitry, or stack several security screens together. While the security level indeed can increase, the circuitry cost increases significantly with each additional security screen layer. In addition, multi-layer or multi-stacking of circuitry leads to reduced flexibility due to added thickness. It may pose reliability issues when wrapping or bending around a board or component.